Authorities have not said whether that blast was also caused by a package bomb or if the victim, like those hit in the two confirmed bombings, is black.
Due to a high level of calls, Manley noted that it may take officers a little while to arrive, but he said "we will respond".
Relatives on the scene identified the woman injured in the third blast as Esperanza Herrera.
The second explosion on Monday happened while police were wrapping up a press conference for the Oldfort Hill explosion. Police said festivalgoers weren't at risk but should be aware of what's happening.
The FBI and ATF are assisting the Austin Police Department with the case, which is being investigated as a homicide.
"We are having innocent people get hurt across this community and it is important that we come together as a community and solve this", said Austin Police Chief Brian Manley at a briefing Monday afternoon.
The chief said all of the victims have been black and that investigators are considering whether race could have factored into the attacks.
Police were processing the scene at the first Monday explosion when the second occurred.
Joanna Samarripa, who lives around the corner, said she saw a woman slumped in the doorway of the home after rushing over moments after the explosion.
The explosion happened hours after a package bombing a few miles away that killed a teenager and seriously injured a woman.More news: Trump says Commerce Secretary will talk tariffs with EU
The house sustained significant damage, according to Chief Manley. "You're going to try to reconstruct what was in the package".
The female's injuries were not life-threatening, he said. Another woman in her 80s had an unrelated medical issue.
On March 2, a 39-year-old man in northeast Austin was killed after a package on his front porch exploded, police said.
Investigators have found no evidence so far of a terrorism link, and have yet to establish a definite motive or profile of the bomber, Manley said. "You knew that something bad was happening", Reynolds said, adding that the victim's body was riddled with holes as emergency responders took her out of the house and into an ambulance. As a result, Austin Police are asking that anyone in the city who finds anything "delivered" to their doorstep not by USPS, FedEx, UPS, or any other major mail carrier report it immediately to the authorities.
A 39-year-old man was killed in the March 2 attack.
In both instances, officials said the explosive packages were left at the doorsteps overnight and the residents opened them in the morning.
A 17-year-old was killed early Monday after bringing a package into his home and opening it, while a woman living at the same address was also injured.
The package detonated early Monday. He died from his injuries shortly after being transported to the hospital, according to KEYE.
Gov. Greg Abbott released a statement condemning the explosions and is offering a $15,000 reward to anyone with information that may lead to an arrest. "That case was being investigated as a suspicious death", he said.